A magnetic disk device having a short servo sector whose circumferential length is shorter than a circumferential length of a normal servo sector has been considered. Servo data read in the short servo sector is less than servo data read in the normal servo sector. Therefore, in the magnetic disk device, for example, the read timing cannot be synchronized by servo address mark, the read timing changes, and the quality of the demodulation process of the short servo sector may be degraded. In addition, burst data is written in a data pattern whose phase is inverted by 180° in one servo track cycle in the radial direction of the disk. Therefore, when burst data is read in a short servo sector, it may be difficult to determine whether the read timing deviates, or whether the read timing deviates in the radial direction.